CVD process for the production of a superconducting fiber bundle

ABSTRACT

Manufacture of superconducting fiber bundle coated with niobium carbonitride by a combination of the CVD process with a plasma activation under a low total gas pressure in which niobium chloride, carbon and nitrogen are reacted to produce the niobium compound which deposits from the gaseous phase on the carrier fiber to form a superconducting layer thereon. The combination of CVD process and plasma activation produces more uniform superconducting layers with smaller grain sizes. The application of an ultrasonic field may be combined with the CVD process. The superconducting layer consists of fine-grained B1-structure niobium compound, the mean grain size of which is between 3 and 50 nm.

This is a division of application Ser. No. 518,381, filed July 29, 1983,U.S. Pat. No. 4,581,289.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of manufacturing a superconductingfiber bundle which contains a multiplicity of carrier fibers such ascarbon fibers, boron fibers, steel fibers, etc. coated with asuperconducting layer of a niobium carbonitride compound.

2. Description of the Prior Art

In the further development of power technology in view of nuclear fusionand superconducting generators, traffic engineering (magnetic suspensionrailroad), environment engineering (coal desulfurization) and highenergy physics, strong-field magnets are required which can bemanufactured economically only on the basis of superconductors.

A new promising superconducting material is, for instance, NbC_(x) N_(y)O_(z) (x+y+z less than or equal to 1), which applied to carrier fibersof a fiber bundle (number of fibers is arbitrary), can be used as afiber conductor. Niobium oxycarbonitride as well as in particularniobium carbonitride in which z=0, are distinguished by high criticaltemperatures, high critical magnetic fields and high critical currentdensities. Any suitable material can be used as the carrier fibermaterial (for instance C, B, steel) which has the necessary mechanicalstrength. It serves as a high-tensile strength matrix and as a substratefor a chemical gaseous phase deposit method (CVD=chemical vapordeposition), in which niobium is deposited by reaction of NbCl₅ with H₂in the presence of carbon and nitrogen-containing gases as a thin film.The CVD process is carried out either in a a single stage (simultaneousNb-deposition and carbonitration) or in two stages (Nb-deposition andcarbonitration following each other in time).

From German Published Prosecuted Application DE-AS No. 28 56 885, a2-stage CVD method has become known which is carried out at gaspressures higher than or equal to normal pressure. In principle, thelayers that can be produced by this method are still too coarse grainedto achieve optimum superconductor properties. The attainable grain sizesof the niobium carbonitride crystals are 50 to 100 nm.

Superconduction parameters such as the upper critical magnetic fieldstrength H_(C2) depend, in addition to the usual influences such ascomposition, degree of order, purity and similar things, particularly onthe metallurgical grain structure. A reduction of the grain size isfollowed, because of the reduction connected therewith of the free pathlength of the conduction electrons, by an increase of theGinsburg-Landau parameter k (k=coherence length/magnetic penetrationdepth) and, since H_(C2) is proportional to k.H_(C) (H_(C) :thermodynamic critical magnetic field strength), an increase of themagnetic field H_(C2) in the thermodynamic critical field H_(C) does notincrease to the same extent in this grains size reduction. In the caseof niobium oxycarbonitride, the thermodynamic properties, particularlythe thermodynamic critical field H_(C), do not react sensitively to afurther reduction as a consequence of a grain size reduction, because oftheir already small free path length of the conduction electrons, sothat in this substance (as also in other B1 structure superconductors)an increase of the magnetic field H_(C2) follow from a reduction of thegrain size.

It was possible to demonstrate this increase of the critical magneticfield strength H_(C2) due to grain size reduction by means of cathodesputtering by which thin niobium oxycarbonitride films were applied toplane carriers (J. R. Gavaler et al, IEEE Transactions on Magnetics,Volume MAG-17, No. 1, January 1981, Pages 573-576). However, it has notbeen possible so far to coat fibers of a carrier fiber bundle withsuperconducting niobium oxycarbonitride with grain sizes of less than 50nm. As was mentioned, only layers, the grain size of which was more than50 nm, could be produced by CVD methods. The cathode sputtering methodon the other hand has a preferred direction, so that the problem ofmutual shading of the individual fibers of the carrier fiber bundlearises. Due to this insufficient throwing power, uniform coating of theindividual fibers has not been possible so far. Plane superconductors,however, can be used technically only with great reservations becausethe eddy currents generated in the ribbons by transversal components ofthe magnetic field never decay and thereby contribute to electricalinstabilities in the ribbon conductor. Otherwise, a reduction of thegrain size is desirable in view of increasing the critical currentdensity J_(C), since the grain boundaries form very effective adhesioncenters for the magnetic flux lines.

SUMMARY OF THE INVENTION

It is an object of the invention to provide methods for manufacturingthe superconducting fiber bundles of the type mentioned at the outsetthrough which a homogeneous coating on all sides of the individualfibers of the fiber bundle is achieved, while the superconducting layerhas high values for the critical magnetic field and the critical currentdensity.

In accordance with the invention, there is provided a method formanufacturing a superconducting fiber bundle formed of a multiplicity ofcarrier fibers coated with a superconducting layer of a niobium compoundof niobium carbonitride of the general formula NbC_(x) N_(y) wherein x+yis equal to or less than 1, said superconductive layer of niobiumcompound having a fine grained B1-structure and a mean grain sizebetween 3 and 50 nm, which comprises reacting niobium chloride, carbonand nitrogen compounds in a CVD (chemical vapor deposition) reactor toproduce the niobium compound, depositing the niobium compound from thegaseous phase on the carrier fiber in the reactor to form asuperconducting layer thereon, maintaining a low total gas pressure ofbetween 0.1 and 5 m bar, and during the deposition using plasmaactivation to effect grain size reduction to said grain size of between3 and 50 nm. There is provided in accordance with the invention a methodfor manufacturing a superconducting fiber bundle formed of amultiplicity of carrier fibers coated with a superconducting layer ofniobium compound of niobium carbonitride of the general formula NbC_(x)N_(y) wherein x+y is equal to or less than 1, said superconductive layerof niobium compound having a fine grained B1-structure and a mean grainsize between 3 and 50 nm, which comprises reacting niobium chloride,carbon and nitrogen compounds in a CVD (chemical vapor deposition)reactor to produce the niobium compound, depositing the niobium compoundfrom the gaseous phase on the carrier fiber in the reactor to form asuperconducting layer thereon, maintaining a total gas pressure belowatmospheric pressure, and carrying out the deposition from the gaseousphase under the action of an ultrasonic field.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a superconducting fiber bundle and method for manufacturing same, itis nevertheless not intended to be limited to the details shown, sincevarious modifications may be made therein without departing from thespirit of the invention and within the scope and range of equivalents ofthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, however, together with additional objects and advantagesthereof will be best understood from the following description when readin connection with the accompanying drawings, in which:

FIG. 1 illustrates part of a coated carrier fiber in a cross-sectionalview showing the surface of the carrier fiber covered withsuperconducting grains of B1-structure niobium compound crystals with agrain size between 3 and 50 nm and grains of insulating material such asNbO₂, and the grains covered by a copper layer.

FIGS. 2 and 3 each show the partial region of a superconducting layercontaining the superconducting grains and insulating material.

FIG. 4 shows a schematic view of a CVD apparatus for NbCN coating ofC-fibers.

FIG. 5 shows a device for fanning-out and coating the carrier fibers andan evaporation device for coating the carrier fiber ribbon.

FIG. 6 is a cross section of the evaporating device taken along lineVI--VI of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

A microstructure of the niobium oxycarbonitride in B1-structure(rock-salt structure) with a mean grain size of between 3 and 50 nm isparticularly advantageous because of the small free path lengthconnected therewith and as was described, the high critical magneticfield strength H_(C2) resulting therefrom.

Niobium oxycarbonitride which has a mean grain size above 50 nm does notmeet the requirement for obtaining very large magnetic fields, since thecritical magnetic field strength H_(C2) as well as the critical currentdensity J_(C) are not sufficient. In crystal structures, on the otherhand, the mean grain size of which is less than 3 nm, an X-ray structureanalysis is no longer possible because of the limited resolution. Beyondthis, the crystalline and thereby also the superconducting propertiesdisappear with decreasing grain size. An advantageous typical mean grainsize for superconducting layers of fiber bundles may, for instance, bearound 10 nm.

Preferably, the layer thickness of the superconducting layer is between100 and 2,000 nm. Such layer thicknesses can be prepared with the methoddescribed in the following and ensure the necessary current carryingcapacity of the fiber bundle. It has been found that the elasticity ofthin, fine-grained layers is higher than that of the thicker and morecoarse-grained layers.

The superconducting layer is preferably coated with a highly conductivemetal layer, for instance of high-purity copper or aluminum, which cantake up the current in the possible event of a failure of thesuperconducting properties (stabilization).

An increase of the current carrying capacity can be achieved bybuilding-in pinning centers. These are inhomogeneities in thesuperconducting material in the order of the coherence length of about 5nm which differ substantially from the superconductive material withrespect to the electrical properties. Grain boundaries are such suitablepinning centers so that the described reduction of the grain size has anadvantageous effect on the current carrying capacity. This applies inany case as long as the H_(C2) value and therewith the electricresistivity of the superconducting grains is low, so that the electricresistivity within the grain is large as compared to the conductivity ofthe grain boundaries. With the presently achieved H_(C2) values, thisdifference of the conductivity is no longer ensured, since the mean-freepath length of the electrons have reached so small a value in the grainthat the mentioned condition (grain conductivity height as compared withthe conductivity of the grain boundary) is no longer met.

Therefore, various structures of the superconducting layer according tothe invention are proposed which show an increase of the difference ofthe conductivity in the grain and at the grain boundary:

1. For reducing the conductivity of the grain boundary it isadvantageous to make the superconducting layer such that occlusions ofinsulating material are contained, uniformly distributed, between theB1-structure niobium oxycarbonitride grains. These occlusions act aspinning centers (pinning grains). The size of the pinning grains is inthe order of magnitude of the coherence length of about 5 nm. Theirconcentration may amount to 50% of the superconducting layer. Insulatingmaterial of interest, are for instance, oxides like ZrO₂, TiO₂, NbO₂ orcarbides such as SiC, NbC or nitrides like TiN.

2. A particularly distinct difference of the conductivity between thegrain and the grain boundary is provided according to a furtheradvantageous embodiment of the invention, if in the superconductinglayer, occlusions of insulating material are deposited at all grainboundary surfaces of the superconducting grains regardless of thespatial orientation of the grain boundary surfaces. Such a skin ofinsulating material at the grain boundary surfaces of thesuperconducting grain has, for instance, a layer thickness of 2 to 5 nm.It is pinning-effective since the normal-conducting core of the fluxtubes can be anchored well in the insulating material.

3. It is further advantageous to deposit occlusions of insulatingmaterial only at the grain boundaries of the superconducting grainswhich have a given spatial orientation within the superconducting layer.This relates to a multilayer structure of the superconducting layer, inwhich superconducting material and insulating material alternate.Although the pinning-effect in such a stratification depends on theorientation of the magnetic field relative to the strata, it isnevertheless found that through preparing such a stratification anadvantageous grain reduction of the superconducting grains can beobtained since the growth of the superconducting grains is alwaysinterrupted by the deposition of the insulating layer. Thesuperconducting and insulating layers may be parallel to the surface ofthe respective carrier fiber. The material and layer thicknesscorrespond to the structure examples described under points 1 and 2.

4. A further advantageous modification of the superconducting layer isprovided if the superconductive material contains, besides niobiumoxycarbonitride, a further element which increases the electricconductivity of the superconducting grain without substantial change ofthe H_(C2) value. Also thereby, the difference of the electricconductivity between grain and grain boundary is increased. Tantalum Taor titanium Ti may, for instance, be used as alloy material.

Particularly advantageous are superconducting layers in which, inaddition to the reduction of the electric conductivity of the grainboundaries by occlusions of insulating material, the conductivity of thesuperconducting grains is increased by the addition of suitableelements, so that large differences of the conductivity between grainand grain boundary result.

A method for producing superconducting fiber bundles according to theinvention has not become known to date. The known CVD processes (forinstance German Published Prosecuted Application DE-AS No. 28 56 885)while they allow homogeneous coating of entire fiber bundles, theattainable grain sizes of the niobium carbonitride crystals are onlyabout 50 to 100 nm and the superconducting layer thicknesses have, as arule, values of less than 100 nm, too thin to ensure sufficient currentcarrying capacity.

Although it is possible to by known physical methods such as reactivecathode atomization (sputtering) to produce an extremely finemicrostructure, these methods have a preferred direction for thecoating, i.e. the back side of a substrate is reached onlyunsatisfactorily, so that layers can be applied only on planesubstrates. Heretofore, it has not been possible to coat fiber bundleswith, for instance, 1000 individual fibers homogeneously, because theinner fibers of the bundle are shaded by the outer fibers.

For the manufacture of superconducting fiber bundles according to theinvention, one can start out from a method in which in a CVD reactor,the niobium oxycarbonitride, particularly the niobium carbonitride, isdeposited by means of chemcial deposition from the gaseous phase throughreaction of niobium chloride, carbon and nitrogen compounds on thecarrier fiber. This can be done on the basis of different known methods.One can start, for instance, from a single-stage as well as a two-stageCVD process (German Published Prosecuted Application DE-AS No. 28 56885). These methods have the advantage of allowing homogeneous coatingof entire fiber bundles. According to the invention, the deposition isaccomplished from the gaseous phase, using plasma activation and/orunder the action of an ultrasonic field which can be generated in theCVD reactor by an inserted ultrasound source which puts the gas invibration. Surprisingly, plasma activation as well as the action ofultrasonic fields in CVD processes, especially in the preparation ofniobium oxycarbonitride layers using a CVD process, lead to aconsiderable reduction of the grain sizes, which can apparently beexplained by disturbances of the growth processes and increasedformation of seeds.

J. R. Hollahan and A. T. Bell have described in "Techniques andApplication of Plasma Chemistry", New York, 1974, the application ofplasmas in chemistry (plasma activation or gas plating) and, among otherthings, the action of plasmas in CVD processes. The objective of themethods explained was to make possible CVD processes by a plasmaactivation, or to lower the process temperature. A reference to grainsize reduction by plasma activation or even a suggestion for utilizingsuch a grain size reduction in the preparation of superconductinglayers, however, is missing. It has furthermore been found that in themethod according to the invention, the deposition rate can be increasedseveral times by plasma activation.

By the example of titanium diboride deposition from TiCl₄ and BCl₃ itwas found by T. Takahashi, H. Itch, Journal of Crystal Growth, Volume 49(1980), pages 445-450, that the fine graininess of the titanium diborideis increased by the ultrasonic action in the CVD process. There, thesubstrate was applied on a vibrator and set in vibration. The object ofthe investigations was to increase the surface hardness of steel toolscoated with titanium diboride. The application of this relatively newprocess to the manufacture of superconductors, particularly ofsuperconducting fiber bundles which cannot be fastened to a vibrator,has not become known from this publication because of the very differentobjective.

The CVD method according to German Published Prosecuted ApplicationDE-AS No. 28 56 885 is carried out at pressures which are higher than orequal to normal pressure in order to avoid contaminations frompenetrating into the deposition apparatus. However, it has been foundthat the use of underpressure offers substantial advantages. Thus, withunderpressure, the coatability of complicated bodies, therefore also thecoatability of fibers can be increased, so that in particular, very goodcoating success has been achieved, especially in fiber bundles with manyfilaments. Total gas pressures between 0.1 and 1000 mbar have been foundto be advantageous. If there are no locks to the outside in the coatingapparatus, the flow of impurities from the outside air can be avoided.If the deposition of niobium oxycarbonitride is carried out in thepresence of a plasma (plasma activation), a total pressure of between0.1 and 5 mbar is preferably set because plasmas are easier to ignite atlow pressure.

In order to place different occlusions of insulating material into thesuperconducting layer, the described CVD process can be modified. Thus,it is advantageous for producing occlusions according to the structuresdescribed under point 1 and 2, if the insulating material is depositedfrom the gaseous phase simultaneously with the niobium oxycarbonitridedeposition. By setting the process parameters such as partial pressures,temperature, coating duration, etc., the grain size of thesuperconducting grains as well as the thickness of the insulatingocclusions can be adjusted. For producing a layer-wise structure of thesuperconducting layer, in which superconducting and insulating layersalternate (see structure according to point 3), the deposition of theinsulating material can be carried out likewise in the CVD reactor forthe niobium oxycarbonitride deposition. The insulating material can bedeposited here alternatingly with the niobium oxycarbonitride from thegaseous phase so that the substrate (carrier fiber) is covered in amanner of onion skins by the superconducting and the insulating layers.

Instead of this alternating deposition, a procedure can be also used forproducing a multilayer structure such that during a continuous CVDdeposition of niobium oxycarbonitride, insulating material is depositedintermittently from the gaseous phase onto the substrate, i.e. withinterruptions in time.

For increasing the electric conductivity, the superconducting grains ofB1-structure niobium oxycarbonitride may contain besides niobium,carbon, nitrogen and oxygen, a further element which increases theconductivity such as tantalum or titanium.

In order to produce such an alloy, one of the CVD processes describedcan be modified such that the element increasing the conductivity can bedeposited in the CVD reactor simultaneously with the niobiumoxycarbonitride deposition.

The fiber coating in the manufacture of superconducting fiber bundlesaccording to the invention may also be based, in spite of problemsmentioned initially, on physical vapor deposition methods throughembodiments according to the invention (for instance sputter processes,reactive sputter processes, ion plating). Such methods are described forinstance, in K. L. Chopra, "Thin Film Phenomena", New York, 1969. Themanufacturing process according to the invention provides that a carrierfiber bundle is fanned out into a carrier fiber ribbon, and thatone-sided or two-sided coating of the carrier fiber ribbon with niobiumoxycarbonitride follows through cathode sputtering, particularlyreactive cathode sputtering, of niobium in the simultaneous presence ofnitrogen or of a nitrogen compound and carbon or a carbon compound,where the carrier fiber ribbon is optionally annealed to deposit theniobium oxycarbonitride in polycrystalline form.

Some of the numerous modifications of the cathode sputtering method willbe listed by way of example in the following:

There are to be distinguished diode or triode arrangements depending onwhether the plasma is ignited automatically or whether it needs anadditional electron source. D-c voltage as well as high frequency a-cvltage can be used. The same fanned-out fiber arrangement also makespossible plasma-activated and reactive evaporation processes. In summaryit can be stated that all methods are suitable which permit influencingthe growth kinetics in a programmed manner, be it via the temperature ofthe substrate, or be it via the kinetic energy of the reactants (plasmaactivation or partial gas pressures).

For influencing the growth kinetics, the carrier fiber canadvantageously be annealed immediately before or during the coating byinfrared radiation. The substrate can also be annealed, for instance, to60°-70° C. The temperature can be controlled by infrared sensors.

To improve the good superconducting properties of the superconductinglayer and also its mechanical properties, a modified process can be usedin which the carrier fiber bundle is fanned-out into a carrier fiberribbon. This is followed by a coating on all sides of the carrier fiberswith the niobium oxycarbonitride by reactive cathode sputtering. Thethermal conditions, particularly the temperature of the carrier fibers,are set to deposit the niobium oxycarbonitride in amorphous form. Asintered niobium oxycarbonitride target is used for exact dosing of thenon-metallic compound partners O₂, N₂ and C. The amorphoussuperconducting layer is converted by a heat treatment following thedeposition (for instance heating to 600 to 800° C.) into a fine grainedB1-structure. By this method, complete freedom from texture (grains showno preferred orientation of any kind) can be achieved, wherefromparticularly good mechanical properties result, in addition to the goodsuperconducting properties.

The fanning-out of the carrier fiber bundle to form a ribbon of fiberslying side by side (linear arrangement of the individual fiber-crosssections) can be performed by the producer or by subsequent debraiding.In such a carrier fiber ribbon, the mutual shading of the individualfibers can largely be avoided, so that a homogeneous coating on allsides of the fibers becomes possible particularly if cathode sputteringis performed on both sides.

The cathode sputtering is advantageously performed reactively, i.e. withthe simultaneous presence of nitrogen or a nitrogen-containing compoundeither in two stages or in one stage, to obtain a conductor as the endproduct which consists of a multiplicity of carrier fibers which arecoated with a niobium carbonitride superconductor of finest grain (3 to50 nm), and a layer thickness in the order of 1000 nm.

Advantageously, the reactive cathode sputtering takes place in afocusing magnetic field (magnetron) by means of which the plasma densityis affected such that the electrons of the plasma are largely kept awayfrom the substrate (fiber bundle). Thereby, undesired heating of thesubstrate is avoided and the grain growth is impeded, whereby theformation of an amorphous initial product is aided.

The conversion of the amorphous initial product into a fine-grainedB1-structure can be accomplished by annealing by means of infraredradiation or another mode of heating, for instance in an oven or by anelectron beam pulse or laser pulse.

As in the described CVD method, occlusions of insulating material canalso be prepared by the physical vapor deposition methods on the grainboundaries of the superconducting grains, or by alloys increasing theconductivity of the superconducting grains. The same procedure asdescribed with the CVD processes is used here analogously.

For preparing occlusions and grain boundary coatings of insulatingmaterial, suitable material can be applied onto the support fiberssimultaneously with a niobium oxycarbonitride in a cathode sputteringreactor. To generate a layer-wise structure, in which super-conductingand insulating layers follow each other alternatingly, the sputtering ofthe insulating material can take place alternatingly with the niobiumoxycarbonitride application in a cathode sputtering reactor. Thesputtering of the insulating material can, however, also be accomplishedin a pulsating manner, while the niobium oxycarbonitride is appliedcontinuously.

To increase the conductivity of the superconducting grains, an elementincreasing the conductivity such as tantalum or titanium, can be admixedwith the source material for the cathode sputtering.

Electric stabilization of the superconducting fibers and contactingsurfaces are provided by coating the fibers with high purity copper oraluminum, preferably after the superconducting layer has been applied tothe carrier fibers by one of the methods described according to theinvention, in a further process step following immediately. This coatingcan be accomplished, for instance, by a chemical process (for instancecurrent-less wet chemical process or CVD method) which makes possiblesimultaneous and uniform copper plating or coating with aluminum of allfibers of the fiber bundle. A thermal post-treatment of the copperimproves its conductivity. If the fiber bundle is fanned out, anelectrolytic coating process or vapor deposition is suitable for coatingwith copper or aluminum, since in this case the individual fibers do notshield or cover each other.

In a further embodiment of the method for manufacturing superconductingfiber bundles the deposition is carried out in a continuous process, inwhich the carrier fibers are unwound from a raw material coil and aretransported through the coating system and the coated fibers are woundon a take-up spool. The method can also be carried out in several steps(for instance two continuous passes through the coating system).Underpressure or subatmospheric pressure or vacuum can be brought aboutby a strong suction of a vacuum pump. The lack of locks in the coatingsystem is of advantage since it avoids the flow-in or impurities fromthe outside air. The two spools can be accommodated in underpressurevessels which can be flanged directly to the coating system withoutlocks.

The invention as well as advantageous further embodiments will beexplained and described, making reference to the drawing.

In FIG. 1, part of the cross section of a carrier fiber 1, for instancea carbon fiber covered with a superconducting layer 2 is schematicallyshown, greatly magnified. The superconducting layer 2 is in turn coveredwith a layer 3 of high-purity copper. The superconducting layer 2consists of a mixture of superconducting grains 4 and grains 5 ofinsulating material. The superconducting grains 4 are B1-structureniobium oxycarbonitride crystals, the grain size of which is between 3and 50 nm, i.e. more than 3 and less than 50 nm, and the chemicalformula of which can be described by NbC_(x) N_(y) O_(z) (x+y+z smallerthan or equal to 1). The insulating grains 5 consist of niobium dioxideNbO₂. However, they may also contain, as mentioned in the introductionto the specification, another oxide, carbide or nitride. The insulatinggrains 5 each have a size which corresponds approximately to thecoherence length of the superconductor. They rest against the grainboundaries of the superconducting grains 4 and act as pinning grains.The thickness of the superconducting layer 2 is between 100 and 2000 nm,i.e. more than 100 and less than 2000 nm.

FIG. 2 shows a partial region of a superconducting layer 2 in which thesuperconducting grains 4 are covered by niobium dioxide or anotherinsulating material 6. The insulating material 6 is depositedsubstantially at all grain boundaries of the B1-structure niobiumoxycarbonitride grains 4, independently of the spatial orientation.

FIG. 3 also shows a partial region of a superconducting layer 2 in whichthe superconducting layer 2 is a stratified structure having alternatelayers of superconducting grains 4 and layers of insulating material 7(for instance niobium dioxide). The occlusions of insulating material 7therefore do not cover all grain boundaries of the B1-structure niobiumoxycarbonitride grains 4 but cover only grain boundaries which have anorientation within the superconducting layer 2 and lie parallel to thesurface 8 of the carrier fiber 1. The superconducting grains 4 ofniobium oxycarbonitride also contain an element 9, for instance tantalumor titanium, which increases the conductivity, which is indicated bydots within the grains 4.

FIG. 4 shows deposition apparatus by means of which a superconductingfiber bundle according to the invention can be manufactured by niobiumoxycarbonitride deposition on carbon fibers and subsequent copperplating of the individual fibers.

In an unwinding chamber 20 is a raw material spool which carries theuncoated carrier fibers 11 (carbon fibers). The carrier fibers 11 arepulled by a fiber transport device 12 through a repeatedly angled-offquartz tube 13 in which the coating of the carrier fibers 22 is carriedout. The coated fibers 14 are then wound on a wind-up coil located in awind-up chamber 15. In the quartz tube 13 there are three gas-inletstubs 16,17, 18 through which nitrogen N₂, a mixture of hydrogen andnitrogen H₂ /N₂ or a mixture of methane an ammonia Ch₄ /NH₃ can beadmitted to the quartz tube 13. The gas contained within the quartz tube13 can be suctioned off through two pump stubs 19, 20, and underpressureproduced in quartz tube 13. The section of the quartz tube 13 which isupstream from the flow direction of fiber 11 from choke point 21 may bemaintained at a pressure different from the section of quartz tube 13which is downstream from choke point 21. Choke point 21 is aconstriction through which the fiber bundle can be pulled but whichprevents pressure equalization in the quartz tube 13 thereby permittingtwo different pressures within the quartz tube 13 before and after thechoke point 21.

During transportation from the unwind chamber 10 to the wind-up chamber15, the fiber bundle passes through four ovens 22, 23, 24, 25. In thefirst oven 22, the carbon fibers 11 are purified if required by beingheated-up in a nitrogen or hydrogen atmosphere. The quantity of gasflowing into the gas inlet stub 16 is, for instance 1 to 20 liters perhour. The oven temperature is set to 600° to 1000° C.

In the second oven 23 (CVD reactor), the fibers are coated with aniobium-containing compound from an NbCl₅ --H₂ --N₂ gas mixture. Forthis purpose, a hydrogen-nitrogen flows through the gas inlet stub 17into the quartz tube 13 with an input quantity which is between 2 and 20liters per hour. The NbCl₅ is converted from a solid evaporator 26,which however, may also be replaced by an evaporator from the liquidphase, into the gaseous phase and is conducted with thehydrogen-nitrogen mixture into the reactor. The temperature of the solidevaporator is set to a value between 80° and 200° C. The niobiumchloride, however, can also be prepared by direct chlorination ofniobium. The temperature of the oven 23 is between 600° and 1000° C. Theresidual gas is pumped-off through the pumping stub 19.

In the third oven 24, the second state of the CVD process for preparingthe superconducting layer takes place. Through the gas-inlet stub 18, acarbon and nitrogen-containing gas mixture (for instance 0 to 50 volumepercent methane, 0 to 50 volume percent ammonia and the remainder,nitrogen) is admitted into the quartz tube 13. The inflow quantity ofmethane and ammonia is each between 2 and 5 liters per hour. The thirdoven 24 is set to a temperature between 700° and 1100° C. In theprocess, the methane and ammonia gases are dissociated and carbon andnitrogen penetrate into the niobium layer. The residual gas is drawn offvia the pumping stub 20.

In principle, the deposition apparatus can also operate single-stage,i.e. niobium is simultaneously deposited in the oven 23 and iscarbonitrated in a carbon and nitrogen-containing atmosphere. The quartztube 13 (reactor) and the gas supply are designed by suitably arrangedflow resistances (choke point 21) and suitable design of the pumps whichare connected to the pumping stubs 19, 20 to effect flow of the gases inthe arrow directions in the ovens 22, 23, 24.

The niobium is deposited in the oven 23 with plasma activation. For thispurpose, the oven 23 is preceded by an RF-coil 27 (according to thedirection of the gas flow in the quartz tube). The RF-coil 27 is fed byan RF-generator 28 with a frequency of 13.65 MHz. The power of theRF-generator 28 is, for instance, between 5 and 100 watts. The coil 27has, for instance, a length of 80 mm, a diameter of 55 mm and carries 13turns. The plasma activation can also be accomplished capacitively or bya d-c discharge, which is not shown. For this purpose, two metal rods orplates which are disposed radially opposite each other are arranged aselectrodes. The reactants (gases) are brought to an excited or ionizedstate within the quartz tube 13 by the RF-coil or the electrodes. Thegas discharge can be excited continuously or pulse-wise.

The niobium deposition in the oven 23 can also take place under theaction of an ultrasonic field. The ultrasonic field can be generated,for instance, by a piezo-crystal 29 which emits soundwaves progressingin the fiber direction. The sound waves are reflected at a soundreflector 30 to effect the development of standing sound waves. It hasbeen found that the development of standing sound waves is not necessaryfor the deposition of niobium and that the ultrasound can also be fed-invia angled-off stubs. Therefore, the quartz tube 13 can also be designedin straight form without angles, whereby several deflections of thefiber bundle can be dispensed with as compared to the depositionapparatus shown. The niobium can be deposited at a sound pressure levelof between 10 and 30 dB and a frequency of between 15 and 20 kHz.

The quartz tube 31 between the solid evaporator 26 and the oven 23 isadvantageously thermally stabilized to maintain the gas temperature.Thermal stabilization indicated by a dash-dotted line 32 may take theform of a heating and cooling jacket and in some instances a covering ofthermal insulation may be adequate.

In the oven 25, the superconducting layers of the fiber bundle arecoated with a highly conductive copper layer. This is accomplished by aCVD process, in which copper is deposited on the fibers from the gaseousphase. The oven 24 can be adjusted so that the fibers are colder thanthe copper to be deposited.

In the following, some process parameters will be listed which areadvantageous for the deposition apparatus shown:

    ______________________________________                                        Temperatures:  .sup.T NbC15(column)                                                                        = 113° C.                                                .sup.T evaporator                                                                           = 138° C.                                                .sup.T oven 22                                                                              = 1000° C.                                               .sup.T oven 23                                                                              = 970° C.                                                .sup.T oven 24                                                                              = 1100° C.                                Pressure:      p             = 0.8 mbar                                       Quantities of  .sup.i 16(N.sub.2)                                                                          = 1.2 lh.sup.-1                                  Gas Inflow:    .sup.i 17(N.sub.2)                                                                          = 2.4 lh.sup.-1                                                 .sup.i 17(H.sub.2)                                                                          = 2.4 lh.sup.-1                                                 .sup.i 18(NH.sub.3)                                                                         = 2.4 lh.sup.-1                                                 .sup.i 18(CH.sub.4)                                                                         = 2.4 lh.sup.-1                                  Fiber Velocity:                                                                              .sup.V fiber  = 6 cm min.sup.-1                                RF- Generator Power:                                                                         N = 40 Watt                                                    RF- Frequency  f = 13.65 MHz                                                  Sound Pressure Level:                                                                        S = 15 dB                                                      Sound Frequency:                                                                             f.sub.S = 18 kHz                                               ______________________________________                                    

In the deposition apparatus according to FIG. 4, a further quartz tube33 is flanged-on at the quartz tube 31 which is located between thesolid evaporator 26 and the oven 23. The zirconium tetrachloride ZrCl₄,water H₂ O and the carrier gas argon Ar can be fed into the depositionapparatus through tube 33. The addition of these gases serves forpreparing grain structures with occlusions of insulating materials(ZrO₂) at the grain boundaries of the superconducting grains. For thispurpose, other compounds can also be fed into the quartz tube 33.Insulating occlusions can be deposited, for instance, by the followingreactions from the gaseous phase.

1. ZrCl₄ +2H₂ O →ZrO₂ +4HCl

2. TiCl₄ +2H₂ O→TiO₂ +4HCl

3. NbCl₄ +H₂ O→NbO₂ +4HCl

4. Si(CH₃)Cl₃ →SiC+ . . .

5. TiCl₄ +CH₄ →TiC+ . . .

6. TiCl₄ +NH₃ →TiN+ . . .

where in principle, the H₂ O can also be produced in the reactions 1 to3 by the reaction

    CO.sub.2 +H.sub.2 →CO+H.sub.2 O

in the reactor. The reaction temperatures are between 1000° and 1100°C., i.e. in the same range as the niobium oxycarbonitride deposition. Acarrier gas (for instance argon) is advantageously admixed to thereaction gases, whereby the dosing and the concentration of the reactiongases in the deposition apparatus can be adjusted with better precision.

The insulating materials can be deposited in different ways inconnection with the niobium oxycarbonitride layer:

1. The deposition of the insulating materials is accomplishedsimultaneously with the niobium oxycarbonitride deposition, by feedingthe corresponding gases into the reactor (oven 23) through the twoquartz tubes 31 and 33. In this process, an insulating deposit isprecipitated on all grain boundaries of the superconducting grains or asa grainy occlusion between the superconducting grains.

2. The deposition of superconducting and insulating material alternates.For such a procedure, a shutoff valve 34 and a shut off valve 35 whichcan be periodically opened and closed in opposite senses, are insertedin the quartz tubes 31 and 33 respectively. The superconducting and theinsulating material are applied to the carrier fiber in layers, forinstance in accordance with FIG. 3.

3. For a layer-wise application of superconducting and insulatinglayers, an operation of the deposition apparatus is also suitable, inwhich the shutoff valve 34 remains open continuously and only theshutoff valve 35 is periodically opened and closed (pulsatingoperation).

Tantalum pentachloride TaCl₅ or titanium tetrachloride TiCl₄ can also beadded through the quartz tube 33 to the reaction mixture simultaneouslyduring the niobium oxycarbonitride deposition. In the CVD deposition,tantalum Ta or titanium Ti, respectively, is deposited in thesuperconducting grains due to this addition. These elements have theproperty of increasing the conductivity of the superconducting grainswithout changing the value of the critical magnetic field H_(C2)substantially.

If the carrier fibers are to be coated by a physical process such asreactive cathode sputtering, the carrier fiber bundle must be fanned-outinto a carrier fiber ribbon, as mentioned at the outset. FIG. 5 shows adevice for fanning-out the carrier fibers 40 to form a carrier fiberribbon 41. The carrier fibers 40 are unwound from several raw materialspools 42 on each of which a multiplicity of parallel carrier fibers 40combined in a carrier fiber bundle are wound and are pulled through afirst comb 43. The comb 43 fans-out the uncoated carrier fibers 40 toform a carrier fiber ribbon 41. Between the first comb 43 and a secondcomb 44, the individual carrier fibers are substantially parallel andare disposed side by side in one plane. In the region of the carrierfiber ribbon 41, the carrier fibers 40 are physically coated with asuperconducting niobium oxycarbonitride layer. Optionally, a coating ofthe fibers with high purity copper or aluminum can also be accomplishedin a region in which the fibers are fanned-out in this manner if aphysical process is to be used for the latter purpose. A deflection roll45 combines the carrier fiber ribbon 41 into a coated fiber bundle 46.The fiber bundle 46 is wound on a take-up reel 47.

Between the two combs 43 and 44, the carrier fiber ribbon 41 passesthrough an evaporation device for coating the carrier fibers 40 with asuperconducting niobium oxycarbonitride layer. The carrier fiber ribbon41 passes through several (four, according to FIG. 5) atomizing systems48, 49, 50, 51, 52, 53, 55 which are shown in FIG. 5 at the edges of thecarrier fiber ribbon for better clarity but are actually arranged onboth sides of the plane defined by the carrier fiber ribbon 41, which isseen in FIG. 6 which shows a cross section VI--VI through two atomizingsystems 48 and 49.

FIG. 6 shows the wall 56 of a reactor which is filled with the carriergas argon Ar at an underpresssure of a few mbar to maintain the plasma.The fanned-out carrier fiber bundle 41 is pulled through the reactor. Onboth sides of the plane defined by the carrier fiber ribbon 41 arearranged two atomizing systems 48, 49. Each atomizing system 48, 49consists of a sintered niobium oxycarbonitride target 59, 60 placed on acathode 57, 58, as well as of an anode 61, 62. The niobiumoxycarbonitride is sputtered in the direction of the arrow. On the sideof the cathode 57, 58 facing away from the carrier fiber ribbon 41 thereis a magnet arrangement 63, 64. The magnet arrangement 63, 64 is shownin cross section. It may be designed, for instance as a ring arrangementin which a south pole S is developed in the center, which is surroundedin ring-fashion by several north poles N. The purpose of this magnetarrangement 63, 64 is to concentrate the plasma immediately in front ofa cathode. The electrons liberated in the sputtering flow either towardthe anodes 61, 62 arranged in the immediate vicinity of the cathode orto the wall 56 of the reactor. The carrier fiber ribbon 41 is exposed tothe material flow of the sputtering material (niobium oxycarbonitride)and only in a small measure to the bombardment by secondary electrons.In this manner, undesirable heating of the substrate (carrier fiberribbon) can be avoided.

For making a multilayer structure of the superconducting layer, theevaporation device consists, as shown in FIG. 5, of several sputteringsystems 48, 49, 50, 51, 52, 53, 54, 55 which are arranged in series. Inthe first and third set of sputtering systems 48, 49, 52, 53, coatingwith niobium oxycarbonitride is accomplished. In the second and fourthset of the sputtering systems 50, 51, 54, 55, the target containsinsulating material so that here, an insulating layer is applied betweeneach two superconducting layers. Insulating materials which may beemployed here (as with the CVD process), are oxides (ZrO₂, TiO₂, NbO₂)carbides (SiC, TiC) or nitrides (TiN).

With the evaporation device described, a superconducting layer can beapplied to the carrier fibers, in which the insulating occlusions aredistributed uniformly in the superconducting layer. For this purpose, asuitable mixed target of niobium carbonitride and a suitable insulatingmaterial is used.

If a mixed target is used which contains, in addition to the niobiumoxycarbonitride, an element such as tantalum Ta or titanium Ti, asuperconducting layer can be produced, the superconducting material ofwhich contains besides the niobium oxycarbonitride, a further elementwhich increases the conductivity of the superconducting grains.

Following the physical coating, the carrier fiber ribbon 41 passesthrough a heat treating device which, according to FIG. 5, is formed bytwo infrared radiators 67, 68 provided with reflectors 65, 66. Thethermal conditions are set so that the amorphous niobium oxycarbonitridecompound which was applied to the carrier fiber ribbon 41 in thesputtering systems 48, 49, 52, 53 is converted into a fine-grainedB1-structure, the average grain size of which is between 3 and 50 nm.The coated fiber bundle is heated, for instance, for about 10 minutes toa temperature of 600° to 800° C.

Thus, the invention relates to a superconducting fiber bundle whichcontains a multiplicity of carrier fibers such as carbon fibers, boronfibers or steel fibers coated with a superconducting layer of a niobiumcompound of the general formula NbC_(x) N_(y) O_(z) (x+y+z less than orequal to 1). In order to obtain high values of the critical magneticfield strength and the critical current, a superconducting layer is usedwhich consists of fine-grained 1-structure niobium oxycarbonitride, themeans grain size of which is between 3 to 50 nm. By plannedincorporation of insulating material into the superconducting layer, theformation of pinning centers can be aided. The niobium compound layer isprepared by means of chemical deposition from the gaseous phase, usingplasma activation and/or an ultrasonic field and optionally,underpressure. As an alternative to the chemical manufacturing method, aphysical method can be used in which a carrier fiber bundle isfanned-out into a carrier fiber ribbon and coating of the carrier fiberson all sides with niobium oxycarbonitride by cathode sputtering follows.Immediately subsequently to the superconducting coating, a furthercoating of the fibers with high-purity copper of aluminum can takeplace.

The foregoing is a description corresponding, in substance, to Germanapplication Nos. P 32 28 729.1, dated July 31, 1982, and P 32 36 896.8dated Oct. 6, 1982, international priority of which is being claimed forthe instant application and which is hereby made part of thisapplication. Any material discrepancies between the foregoingspecification and the specification of the aforementioned correspondingGerman applications are to be resolved in favor of the latter.

We claim:
 1. Method for manufacturing a superconducting fiber bundleformed of a multiplicity of carrier fibers coated with a superconductinglayer of a niobium compound of niobium carbonitride of the generalformula NbC_(x) N_(y) wherein x+y is equal to or less than 1, saidsuperconductive layer of niobium compound having a fine grainedB1-structure and a mean grain size between 3 and 50 nm, which comprisesreacting niobium chloride, carbon and nitrogen compounds in a CVD(chemical vapor deposition) reactor to produce the niobium compound,depositing the niobium compound from the gaseous phase on the carrierfiber in the reactor to form a superconducting layer thereon,maintaining a low total gas pressure of between 0.1 and 5 m bar, andduring the deposition using plasma activation to effect grain sizereduction to said grain size of between 3 and 50 nm, whereinprecipitations of insulating material are uniformly distributed betweenthe B1-structure niobium compound grains of the superconducting layer bydepositing the insulating material from the gaseous phase in the CVDreactor simultaneously with the niobium compound deposition.
 2. Methodfor manufacturing a superconducting fiber bundle formed of amultiplicity of carrier fibers coated with a superconducting layer ofniobium compound of niobium carbonitride of the general formula NbC_(x)N_(y) wherein x+y is equal to or less than 1, said superconductive layerof niobium compound having a fine grained B1-structure and a mean grainsize between 3 and 50 nm, which comprises reacting niobium chloride,carbon and nitrogen compounds in a CVD (chemical vapor deposition)reactor to produce the niobium compound, depositing the niobium compoundfrom the gaseous phase on the carrier fiber in the reactor to form asuperconducting layer thereon, maintaining a total gas pressure belowatmospheric pressure, and carrying out the deposition from the gaseousphase under the action of an ultrasonic field, wherein precipitations ofinsulating material are uniformly distributed between the B1-structureniobium compound grains of the superconducting layer by depositing theinsulating material from the gaseous phase in the CVD reactorsimultaneously with the niobium compound deposition.
 3. Method formanufacturing a superconducting fiber bundle formed of a multiplicity ofcarrier fibers coated with a superconducting layer of a niobium compoundof niobium carbonitride of the general formula NbC_(x) N_(y) wherein x+yis equal to or less than 1, said superconductive layer of niobiumcompound having a fine grained B1-structure and a mean grain sizebetween 3 and 50 nm, which comprises reacting niobium chloride, carbonand nitrogen compounds in a CVD (chemical vapor deposition) reactor toproduce the niobium compound, depositing the niobium compound from thegaseous phase on the carrier fiber in the reactor to form asuperconducting layer thereon, maintaining a low total gas pressure ofbetween 0.1 and 5 m bar, and during the deposition using plasmaactivation to effect grain size reduction to said grain size of between3 and 50 nm, wherein precipitations of insulating material are depositedfrom the gaseous phase in the CVD reactor in the superconducting layeron all grain boundaries of the B1-structure niobium compound grains,independently of their spatial orientation, simultaneously with theniobium compound deposition.
 4. Method for manufacturing asuperconducting fiber bundle formed of a multiplicity of carrier fiberscoated with a superconducting layer of niobium compound of niobiumcarbonitride of the general formula NbC_(x) N_(y) wherein x+y is equalto or less than 1, said superconductive layer of niobium compound havinga fine grained B1-structure and a mean grain size between 3 and 50 nm,which comprises reacting niobium chloride, carbon and nitrogen compoundsin a CVD (chemical vapor deposition) reactor to produce the niobiumcompound, depositing the niobium compound from the gaseous phase on thecarrier fiber in the reactor to form a superconducting layer thereon,maintaining a total gas pressure below atmospheric pressure, andcarrying out the deposition from the gaseous phase under the action ofan ultrasonic field, wherein precipitations of insulating material aredeposited from the gaseous phase in the CVD reactor in thesuperconducting layer on all grain boundaries of the B1-structureniobium compound grains, independently of their spatial orientation,simultaneously with the niobium compound deposition.
 5. Method formanufacturing a superconducting fiber bundle formed of a multiplicity ofcarrier fibers coated with a superconducting layer of a niobium compoundof niobium carbonitride of the general formula NbC_(x) N_(y) wherein x+yis equal to or less than 1, said superconductive layer of niobiumcompound having a fine grained B1-structure and a mean grain sizebetween 3 and 50 nm, which comprises reacting niobium chloride, carbonand nitrogen compounds in a CVD (chemical vapor deposition) reactor toproduce the niobium compound, depositing the niobium compound from thegaseous phase on the carrier fiber in the reactor to form asuperconducting layer thereon, maintaining a low total gas pressure ofbetween 0.1 and 5 m bar, and during the deposition using plasmaactivation to effect grain size reduction to said grain size of between3 and 50 nm, wherein precipitations of insulating material are depositedfrom the gaseous phase at grain boundaries of the B1-structure niobiumcompound grains with definite spatial orientation within thesuperconducting layer in which the grain boundaries are parallel to thesurface of the respective carrier fiber, and wherein the niobiumcompound and the insulating material are deposited from the gaseousphase alternatingly.
 6. Method for manufacturing a superconducting fiberbundle formed of a multiplicity of carrier fibers coated with asuperconducting layer of niobium compound of niobium carbonitride of thegeneral formula NbC_(x) N_(y) wherein x+y is equal to or less than 1,said superconductive layer of niobium compound having a fine grainedB1-structure and a mean grain size between 3 and 50 nm, which comprisesreacting niobium chloride, carbon and nitrogen compounds in a CVD(chemical vapor deposition) reactor to produce the niobium compound,depositing the niobium compound from the gaseous phase on the carrierfiber in the reactor to form a superconducting layer thereon,maintaining a total gas pressure below atmospheric pressure, andcarrying out the deposition from the gaseous phase under the action ofan ultrasonic field, wherein precipitations of insulating material aredeposited from the gaseous phase at grain boundaries of the B1-structureniobium compound grains with definite spatial orientation within thesuperconducting layer in which the grain boundaries are parallel to thesurface of the respective carrier fiber, and wherein the niobiumcompound and the insulating material are deposited from the gaseousphase alternatingly.
 7. Method for manufacturing a superconducting fiberbundle formed of a multiplicity of carrier fibers coated with asuperconducting layer of a niobium compound of niobium carbonitride ofthe general formula NbC_(x) N_(y) wherein x+y is equal to or less than1, said superconductive layer of niobium compound having a fine grainedB1-structure and a mean grain size between 3 and 50 nm, which comprisesreacting niobium chloride, carbon and nitrogen compounds in a CVD(chemical vapor deposition) reactor to produce the niobium compound,depositing the niobium compound from the gaseous phase on the carrierfiber in the reactor to form a superconducting layer thereon,maintaining a low total gas pressure of between 0.1 and 5 m bar, andduring the deposition using plasma activation to effect grain sizereduction to said grain size of between 3 and 50 nm, whereinprecipitations of insulating material are deposited from the gaseousphase at grain boundaries of the B1-structure niobium compound grainswith definite spatial orientation within the superconducting layer, andwherein the insulating material is deposited pulsewise from the gaseousphase in the CVD reactor while the niobium compound is depositedcontinuously.
 8. Method for manufacturing a superconducting fiber bundleformed of a multiplicity of carrier fibers coated with a superconductinglayer of niobium compound of niobium carbonitride of the general formulaNbC_(x) N_(y) wherein x+y is equal to or less than 1, saidsuperconductive layer of niobium compound having a fine grainedB1-structure and a mean grain size between 3 and 50 nm, which comprisesreacting niobium chloride, carbon and nitrogen compounds in a CVD(chemical vapor deposition) reactor to produce the niobium compound,depositing the niobium compound from the gaseous phase on the carrierfiber in the reactor to form a superconducting layer thereon,maintaining a total gas pressure below atmospheric pressure, andcarrying out the deposition from the gaseous phase under the action ofan ultrasonic field, wherein precipitations of insulating material aredeposited from the gaseous phase at grain boundaries of the B1-structureniobium compound grains with definite spatial orientation within thesuperconducting layer, and wherein the insulating material is depositedpulsewise from the gaseous phase in the CVD reactor while the niobiumcompound is deposited continuously.
 9. Method for manufacturing asuperconducting fiber bundle formed of a multiplicity of carrier fiberscoated with a superconducting layer of a niobium compound of niobiumcarbonitride of the general formula NbC_(x) N_(y) wherein x+y is equalto or less than 1, said superconductive layer of niobium compound havinga fine grained B1-structure and a mean grain size between 3 and 50 nm,which comprises reacting niobium chloride, carbon and nitrogen compoundsin a CVD (chemical vapor deposition) reactor to produce the niobiumcompound, depositing the niobium compound from the gaseous phase on thecarrier fiber in the reactor to form a superconducting layer thereon,maintaining a low total gas pressure of between 0.1 and 5 m bar, andduring the deposition using plasma activation to effect grain sizereduction to said grain size of between 3 and 50 nm, wherein anadditional element is added to the superconductive material of niobiumcompound to increase its conductivity by depositing the element from thegaseous phase in the CVD reactor simultaneously with the niobiumcompound deposition.
 10. Method for manufacturing a superconductingfiber bundle formed of a multiplicity of carrier fibers coated with asuperconducting layer of niobium compound of niobium carbonitride of thegeneral formula NbC_(x) N_(y) wherein x+y is equal to or less than 1,said superconductive layer of niobium compound having a fine grainedB1-structure and a mean grain size between 3 and 50 nm, which comprisesreacting niobium chloride, carbon and nitrogen compounds in a CVD(chemical vapor deposition) reactor to produce the niobium compound,depositing the niobium compound from the gaseous phase on the carrierfiber in the reactor to form a superconducting layer thereon,maintaining a total gas pressure below atmospheric pressure, andcarrying out the deposition from the gaseous phase under the action ofan ultrasonic field, wherein an additional element is added to thesuperconductive material of niobium compound to increase itsconductivity by depositing the element from the gaseous phase in the CVDreactor simultaneously with the niobium compound deposition.
 11. Methodaccording to claim 1, wherein after the superconducting layer is appliedto the carrier fibers, the fibers are coated with a metal selected fromthe group consisting of high-purity copper and aluminum in a furtherprocess step immediately following thereon.
 12. Method for manufacturinga superconducting fiber bundle formed of a multiplicity of carrierfibers coated with a superconducting layer of a niobium compound ofniobium carbonitride of the general formula NbC_(x) N_(y) wherein x+y isequal to or less than 1, said superconductive layer of niobium compoundhaving a fine grained B1-structure and a mean grain size between 3 and50 nm, which comprises reacting niobium chloride, carbon and nitrogencompounds in a CVD (chemical vapor deposition) reactor to produce theniobium compound, depositing the niobium compound from the gaseous phaseon the carrier fiber in the reactor to form a superconducting layerthereon, maintaining a low total gas pressure of between 0.1 and 5 mbar, and during the deposition using plasma activation to effect grainsize reduction to said grain size of between 3 and 50 nm.
 13. Method formanufacturing a superconducting fiber bundle formed of a multiplicity ofcarrier fibers coated with a superconducting layer of niobium compoundof niobium carbonitride of the general formula NbC_(x) N_(y) wherein x+yis equal to or less than 1, said superconductive layer of niobiumcompound having a fine grained B1-structure and a mean grain sizebetween 3 and 50 nm, which comprises reacting niobium chloride, carbonand nitrogen compounds in a CVD (chemical vapor deposition) reactor toproduce the niobium compound, depositing the niobium compound from thegaseous phase on the carrier fiber in the reactor to form asuperconducting layer thereon, maintaining a total gas pressure belowatmospheric pressure, and carrying out the deposition from the gaseousphase under the action of an ultrasonic field.